Methanol and silicon monoxide observations toward bipolar outflows associated with Class 0 objects

We report Swedish-ESO Submillimetre Telescope observations of seven bipolar outflows thought to be associated with Class 0 objects in the upsilon=0 J=3-->2 and J=2-->1 transitions of SiO and J(k)= 3(k)-->2(k) and J(k)=2(k)-->1k transitions of CH3OH. Methanol and silicon monoxide emission from outflowing gas were detected toward the lobes of four objects (NGC 2264G, IRAS 16293-2422, Serpens S68N, and Serpens SMM 4). The SiO line profiles are characteristics of C-type bow shocks, showing a peak at a radial velocity close to but displaced from the ambient cloud velocity and a gradual decrease in intensity from the peak toward higher flow velocities. There is a significant correlation between the column density of SiO and the terminal SiO flow velocity, which suggests a velocity-selective enhancement in the production of SiO molecules. We find that the SiO abundance in the lobes is enhanced with respect to that of the ambient cloud by a factor of at least 330 in IRAS 16293-2422 and SMM 4, 170 in NGC 2264G, and 80 in S68N. The abundance is enhanced by a factor of 500 in CH 3 OH IRAS 16293-2422, 330 in SMM 4, 80 in S68N, and 23 in NGC 2264G. In addition, we find that the dependence of the SiO/CO and CH3OH/CO abundance ratios with radial flow velocity shows a steep increase in the range from similar to0 to similar to4-5 km s(-1) and a gradual decline toward higher flow velocities. In the remaining three sources (CG 30, IRAS 13036-7644, and VLA 1623-243), emission in methanol was detected from a narrow line at the velocity of the ambient cloud, and no emission was detected in silicon monoxide. Weak methanol emission from a low-velocity outflow component was detected toward CG 30.